The towed pinger locator is deployed off the deck of the Ocean Shield.

ADF: Leut Kelly Lunt

The US Navy has moved to dismiss comments from one of its officials who said pings thought to have come from MH370's black box were probably emitted by the search ship itself.

The "pings" prompted a multi-national search that has covered 4.64 million square kilometres of ocean but has found no sign of wreckage from the missing Malaysia Airlines flight.

The US Navy's deputy director of ocean engineering Michael Dean told CNN there was now broad agreement the signals came from some other man-made source unrelated to the jet that disappeared on March 8 carrying 239 people, six of them Australians.

"Our best theory at this point is that [the pings were] likely some sound produced by the ship... or within the electronics of the towed pinger locator," Mr Dean said.

"Your fear any time you put electronic equipment in the water is that if any water gets in and grounds or shorts something out, that you could start producing sound."

But the US Navy has since issued a statement calling Mr Dean's comments "speculative and premature".

"The US has been working cooperatively with our Malaysia, Australian and international partners for more than two months in an effort to locate MH370," a spokesman said.

"Mike Dean's comments today were speculative and premature, as we continue to work with our partners to more thoroughly understand the data acquired by the towed pinger locator.

"As such, we would defer to the Australians, as the lead in the search effort, to make additional information known at the appropriate time."

Mr Dean told CNN it was not possible to absolutely exclude that the pings came from the black boxes, but there was no evidence now to suggest they did.

The US Navy pinger locator, dragged by the Australian ship Ocean Shield, was used by searchers to listen for underwater signals in the remote southern Indian Ocean in an area where satellite data suggested the plane went down.

A series of signals the ship picked up promoted Prime Minister Tony Abbott to say he was "very confident" they were from the black box from the plane that vanished en route from Kuala Lumpur to Beijing.

When asked whether the other countries involved in the search, which is being led by Australia, had reached the same conclusion about the pings not coming from the black boxes, Mr Dean said "Yes".

Eight nations have been involved in the unprecedented hunt - Australia, the United States, New Zealand, Malaysia, Japan, South Korea, Britain and China.

After almost two months without finding any wreckage, the current underwater search has been narrowed to a small area around the location in which one of four acoustic signals, which were believed to be from the plane's black box recorders, was detected on April 8.

A United States Navy deep-sea autonomous underwater vehicle (AUV) has been scouring a remote stretch of the Indian Ocean floor near where one of the pings was believed to have originated from.

Officials from Australian, Chinese or Malaysian search operations are yet to comment whether they believe the pings, which prompted the search, are unrelated to the jet.